We’ve long since passed the point where it’s noteworthy when polling data shows a Democrat faring better with female voters than a Republican. The partisan gender gap has been evident in every national election since 1980, when Ronald Reagan essentially settled for a tie with Jimmy Carter among women, while crushing him among men by nearly 20 points.

It is news, though, when the male/female split suddenly widens and emerges as the potentially decisive factor in a presidential race. And while it’s still early, that may be where we are in the 2012 campaign.

A new USA Today/Gallup poll of 12 battleground states shows that Barack Obama actually trails Mitt Romney by one point among men. But among women, the president is ahead by 18 – giving him an overall lead of nine points, 51 to 42 percent, in the battleground venues. This is a dramatic shift from mid-February, when the same poll put Romney ahead of Obama by two points. The difference is an exploding gender gap that can be isolated to a specific segment of the female voting universe:

The biggest change came among women under 50. In mid-February, just under half of those voters supported Obama. Now more than six in 10 do while Romney’s support among them has dropped by 14 points, to 30%. The president leads him 2-1 in this group.